No. 377-] THE ORIGIN OF THE MAMMALIA. 321 
zontal palatine and maxillary plates, and two (exoccipital) con- 
dyles complete the mammalian facies. 
The origin of the paired occipital condyles of the Mammalia 
is a matter of great importance. We observe a tripartite con- 
dyle in Dicynodon and in the Chelonia, into which the basi- and 
exoccipitals enter about equally; certain types of Lacertilia, 
such as Uroplates and Gecko (fide Cope), also evidently acquired 
their bipartite condyles second- 
arily by the recession of the 
median basioccipital element. 
It would appear, therefore, that 
the theriodonts, in which this 
median basioccipital element is 
still quite prominent, also ac- 
quired the paired exoccipital 
condyle in the same manner, 
t.e., secondarily, or from the 
tripartite type, such as that 
seen in Dicynodon. We would 
thus have the explanation of 
the development of this paired 
structure from a reptilian tri- 
partite condyle, as in Huxley’s 
original conjecture, rather than 
directly from an amphibian Fic. 8.— External and anterior views of the 
: ° sP Pove girdle, supposed to belong to 
paired condyle, for in the Am- brauta aonar the a parts of 
phibia the paired condition of = onnen pP ~~ 
the condyles arises in an ex- 
tremely early period, rather than by a secondary recession 
of the basioccipital element. 
Of the transitional characters of Cynognathus, the reduced 
and overlapped quadrate is what we should expect to find in a 
promammal upon the Albrecht-Cope-Baur theory that the quad- 
rate in the mammalia is fused with the squamosal. Among the 
reptilian characters are the separate prefrontal and postfrontal 
elements (the postorbitals being united with the malars), as well 
as the constitution of the lower jaw out of distinct elements 
(angular, articular, dentary, splenial), which by reduction and 
